As a conventional touch detecting device of a keyboard instrument, there has been known one disclosed e.g. in Patent Literature 1. This keyboard instrument is an upright automatic performance piano, and is comprised of pivotally movable keys (not shown) and hammers 63 each of which pivotally moves in accordance with depression of an associated key to strike an associated string 62, as shown in FIG. 14. As shown in FIG. 14, the touch detecting device 61 includes a shutter 64 attached to an associated one of the hammers 63, and first to third sensors 65 to 67. The shutter 64 is in the form of a plate shape, and extends upward along a catcher shank 63a of the hammer 63 in a state secured to the same. The shutter 64 has an upper edge part thereof formed with first to third steps 64a, 64b, and 64c in a manner forming stairs. The first step 64a is highest, and the third step 64c is lowest.
The first to third sensors 65 to 67 are arranged adjacent to each other in a manner corresponding to the respective first to third steps 64a to 64c, and each of the sensors 65 to 67 is comprised of a pair of a light emitting part and a light receiving part (neither of which is shown). The light emitting parts are disposed on one side of a traveling path of the shutter 64, and the light receiving parts are disposed on the other side of the traveling path in facing relation to the respective associated light emitting parts so as to receive light emitted therefrom. In a key released state (a position indicated by solid lines in FIG. 14), the shutter 64 is positioned below the first to third sensors 65 to 67 without overlapping them.
With this arrangement, as the hammer 63 pivotally moves about a center pin 68 in a counterclockwise direction, as viewed in FIG. 14, in accordance with key depression, the shutter 64 pivotally moves along with the hammer 63. In accordance with this pivotal motion, the first step 64a of the shutter 64 reaches the first sensor 65, whereby light from the light emitting part is blocked to prevent light reception by the associated light receiving part. When the hammer 63 further moves pivotally, light from the light emitting part of the second sensor 66 is blocked to prevent light reception by the associated light receiving part, and when the hammer 63 further moves pivotally, light from the light emitting part of the third sensor 67 is blocked to prevent light reception by the associated light receiving part. On the other hand, when the key is released, the states of blocking light from the light emitting parts are released in the reverse order to the above, whereby the light receiving parts of the respective sensors return to the light receiving states.
The first to third sensors 65 to 67 each output a “Low” signal as a detection signal when the amount of light received by a light receiving part thereof is not lower than a predetermined level, while they each output a “High” signal as a detection signal when the amount of light is lower than the predetermined level. The detection signal from the first sensor 65 is used for detection of key depression or key release. Specifically, timing in which the detection signal changes from “Low” to “High” (hereinafter referred to as “the light shielding timing”) is detected as key depression timing, and timing in which the detection signal changes from “High” to “Low” (hereinafter referred to as “the light receiving timing”) is detected as key release timing. On the other hand, the detection signals from the second and third sensors 66 and 67 are used for detection of a key depression speed. Specifically, the depression speed of a key is determined based on a time lag between the light shielding timing of the second sensor 66 and that of the third sensor 67.
However, in this conventional touch detecting device 61, the light emitting parts of the respective first to third sensors 65 to 67 are arranged adjacent to each other on one side of the traveling path of the shutter 64, and the associated light receiving parts are arranged adjacent to each other on the other side of the traveling path. Therefore, when light beams emitted from the respective light emitting parts are divergent, each of the light beams diffuses as approaching the associated light receiving part, and hence the light emitting part of the first sensor 65, for example, receives not only light from the light emitting part of the first sensor 65, but also light from the light emitting part of the adjacent second sensor 66.
FIG. 15 schematically shows the above-mentioned situation. More specifically, as shown in FIG. 15(a), since a light beam from a light emitting part SO1a of a first sensor SO1 is divergent, the light beam reaches not only a light receiving part SO1b of the first sensor SO1, but also a light receiving part SO2b of a second sensor SO2. For this reason, as shown in FIG. 15(b), even in a state where the light beam from the light emitting part SO1a of the first sensor SO1 is blocked by a shutter S, the light receiving part SO1b of the first sensor SO1 receives a light beam from a light emitting part SO2a of the second sensor SO2. As a consequence, in the conventional touch detecting device 61, the light shielding timing of the first sensor 65 delays during key depression, whereas during key release, the light receiving timing advances. This makes it impossible to detect key depression timing or key release timing with accuracy. Further, in detecting the key depression speed, the light shielding timing of the second sensor 66 delays, whereas that of the third sensor 67 does not delay because the third sensor 67 is not affected by light from the light emitting part of the second sensor 66. As a result, the time lag between the two light shielding timings becomes smaller than the difference between actual passage times of the shutter 64, and therefore the detected key depression speed becomes larger than the actual key depression speed. Thus, the key depression speed cannot be accurately detected.
Further, a degree of deviation in each of the light shielding timing and the light receiving timing varies according to the position of passage of the shutter 64 between the light emitting parts of the first to third sensors 65 to 67 and the light receiving parts of the first to third sensors 65 to 67. FIG. 16 schematically shows this situation. More specifically, when the position of passage of the shutter 64 is close to the light receiving parts SO1b and SO2b as shown in FIG. 16(a), light from the second sensor SO2 is more readily blocked, making it difficult for the light to reach the light receiving part SO1b of the first sensor SO1, which reduces the degree of deviation in each of the light shielding timing and the light receiving timing. On the other hand, when the position of passage of the shutter 64 is close to the light emitting parts SO1a and SO2a as shown in FIG. 16(b), the light from the second sensor SO2 cannot be readily blocked, making it easier for the light to reach the light receiving part SO1b of the first sensor SO1, which increases the degree of deviation in each of the light shielding timing and the light receiving timing. As described above, the degree of deviation in each of the light shielding timing and the light receiving timing varies according to the position of passage of the shutter 64, and therefore the key depression and release timings and the key depression speed, which are detected based on the light shielding timing and the light receiving timing, also vary according to the position of passage of the shutter 64.
The above-mentioned problems can be solved by increasing the distances between the first to third sensors 65 to 67 to such an extent as will prevent each light receiving part thereof from being affected by light from the light emitting part of the other sensors. In this case, however, not only degradation of the mounting density of the sensors, but also an increase in the distance between the second and third sensors 66 and 67, i.e. an increase in the length of a key depression speed-detecting section is caused, which makes it impossible to accurately detect e.g. a key depression speed immediately before the hammer 63 strikes the string 62, which is important as key depression information. Alternatively, it can also be envisaged to solve the above-mentioned problems e.g. by reducing the intensity of light emission from the light emitting parts of the first to third sensors 65 to 67 to such a level as will prevent each light receiving part thereof from being affected by light from the light emitting part of the other sensors. In this case, however, the total amount of light received by the light receiving part is reduced, and hence, even though a light receiving part is in the light receiving state, the amount of light received by the light receiving part sometimes becomes lower than a predetermined level, which causes instability of the detection signal and thereby considerably degrades the accuracy of detection of the key depression and release timings and that of detection of the key depression speed.
The present invention has been made in order to solve the above problems, and an object thereof is to provide a touch detecting device of a keyboard instrument, which makes it possible not only to enhance the mounting density of a plurality of optical sensors, but also to detect touch information of a key with high accuracy without being affected by light from the other optical sensors.
[Patent Literature 1] Japanese Laid-Open Patent Publication (Kokai) No. H02-160292